Process for depositing boron carbide



Nov. 25, 1969 J. J. GEBHARDT 3,480,467

PROCESS FOR DEPOSITING BORON CARBIDE Filed March 30. 1966 76 Vo/fge Source INVENTOR. JOSEPH J. GEBHARDT 9% 7 M Gd United States Patent 3,480,467 PROCESS FOR DEPOSITING BORON CARBIDE Joseph J. Gebhardt, Malvern, Pa., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Mar. 30, 1966, Ser. No. 538,933 Int. Cl. C23c 13/02 US. Cl. 117-93 3 Claims ABSTRACT OF THE DISCLOSURE A process for depositing boron carbide on a substrate by heating a substrate to a temperature of about 1215 degrees C. while in an enclosed chamber containing a container of ethyl decaborane and while the pressure within said enclosed chamber is reduced to between about 0.1 and 0.5 mm. of mercury whereby ethyl decaborane vaporizes and boron carbide is deposited upon the substrate.

The present invention relates to a process for depositing a refractory material on a substrate and more particularly to a process for depositing boron carbide on a substrate.

Various refractory materials are frequently deposited on substrates, such as metals, to provide increased life to the substrates, particularly when they are placed in detrimental atmospheres or subjected to elevated temperatures. One refractory material that has been found to provide an effective diffusion barrier is boron carbide, however, heretofore known methods of depositing boron carbide on substrates have had shortcomings. A heretofore known method of depositing boron carbide requires a complex series of reactions involving the decomposition of methane and boron trichloride at elevated temperatures.

The present invention provides a relatively simple process for depositing boron carbide on substrates by thermally decomposing ethyl decaborane in a vacuum chamber while heating the article to be coated.

It is therefore a general object of the present invention to provide an improved method of applying a refractory coating to a substrate.

Another object of the present invention is to provide an improved method for depositing boron carbide on a metallic substrate.

Other objects and advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein the figure is a diagrammatic view showing apparatus for carrying out the process of the present invention.

Referring now to the drawing, a container 11 is provided and, by way of example, container 11 might be made of heat-resisting glass, such as Pyrex. An open end of container 11 is enclosed by a stopper 12, which is made of electrically insulating material, and a pair of electrodes 13 and 14 are passed through stopper 12 and extend into the chamber 15 of container 11. Electrodes 13 and 14 are connected to a suitable voltage source through leads 16 and 17, respectively. A tube 18 connects container 11 to a vacuum pump through a valve 19.

An article to be coated, such as a piece of tungsten wire 21, is connected between electrodes 13 and 14 and a container 22 holding a quantity of ethyl decaborane 23 is positioned beneath the article to be coated.

3,480,467 Patented Nov. 25, 1969 ICC The following may be cited as specific examples of the practice of this invention:

EXAMPLE I A three inch piece of tungsten wire .025 inch in diameter was connected between electrodes 13 and 14. Approximately 2.5 cc. of ethyl decaborane C H B H was placed in container 22 and container 11 was then sealed and evacuated to a pressure of about 0.l mm. of mercury. Current was then applied to the tungsten wire from a DC. power supply until a temperature of about 1215 degrees C. was reached. After about 1-0 minutes, the pressure in container 11 built up to about 5 mm. at which time container 11 was again evacuated. This pressure build-up was presumably due to hydrogen release by the decomposition of the ethyl decaborane. After about a total time of 40 minutes, the current was turned off and the tungsten wire was removed. The tungsten wire had been coated to a thickness of about .005 inch with a grayish substance that was brittle and very hard. This substance was identified by X-ray diffraction as boron carbide, B C. During the period of the experiment, a slight deposit of yellowish material characteristic of high molecular weight borane tars formed on the walls of the reactor.

EXAMPLE II In another experiment, the procedure of Example I was carried out on a piece of tungsten wire .010 inch in diameter. Boron carbide, B C, was again deposited onto the wire. Micrographs of the cross section of the tungsten wire showed that little, if any, attack on the tungsten wire had occurred.

What is claimed is:

1. A process for the decomposition of boron carbide upon a substrate comprising:

placing said substrate in an enclosed chamber containing a container of ethyl decaborane, and then heating said substrate to temperature of about 1215 degrees C. while the pressure within said enclosed chamber is maintained between about 0.1 mm. of mercury and about 5 mm. of mercury whereby said ethyl decaborane vaporizes and boron carbide is deposited upon said substrate.

2. A process for the deposition of boron carbide as set forth in claim 1 wherein said substrate is tungsten wire.

3. A process for the deposition of boron carbide as set forth in claim 2 wherein said tungsten wire is heated by passing an electric current therethrough.

References Cited UNITED STATES PATENTS 2,484,519 10/1949 Martin 117106 3,142,707 7/1964 Obenland 260-606.5 3,347,931 10/ 1967 Wunz et al. 260--606.5 3,398,013 8/1968 Krochmal et a1 117-106 OTHER REFERENCES Coates, Organo-Metallic Compounds, 1960, pp. 94 to 98 relied upon.

ANDREW G. GOLIAN, Primary Examiner US. Cl. X.R. 

